3. Reading two-column PDFs in web browsers really, really sucks. You can't fit one column on the screen given the type size, and then you end up scrolling down the first column, scrolling up to the top of the page to the second column, then going back to the first column for the next page, etc. PDF reading programs, *please* rip these PDFs apart on the fly and make them single-column. You'll make us all a lot happier.

4. iPhone can't tap-zoom when rendering PDFs. I assume they have some structure detection algorithms for HTML. Adding bitmap box/column detection for PDFs shouldn't be that hard.